1. Field of the Invention
The present invention relates to an electrical machine, which is reversible as a starter and generator for an internal combustion engine, especially an internal combustion engine of a motor vehicle. Such machines have been developed because they make it possible to unite the two functions of starting the engine and generating electrical current, which is needed. for the on-board systems of a vehicle, such as ignition, lighting, and so forth, in a single electrical machine and thus to save both weight and expense.
2. Description of the Related Art
In such electrical machines, however, the problem arises that for the generator mode and the starter mode of the electrical machine, different gear ratios are needed, so that a reversible gear must be provided that makes it possible to generate these different gear ratios in accordance with whichever function of the electrical machine is required just at that time.
A two-stage planetary gear is known from German Patent Disclosure DE 36 04 395. This reference teaches the use of such a gear in an automatic transmission of a motor vehicle for setting various gear ratios that correspond to the various gears, that is, speeds, in gear shifting and act on the chassis of the motor vehicle. The force transmission is always in the same direction here, namely from the engine to the chassis. This reference provides no information on the starter or the generator of the vehicle.
Another example of a two-stage planetary gear is known from German Patent Disclosure DE 19 531 043 A1. The planetary gear discussed in this reference is intended to be driven by a motor, in particular a motor of an electrical power tool, such as a power drill, and is intended to drive a tool with an adjustable gear ratio. Only one of the two stages is assigned a locking device that can prevent any rotation of the ring gear of this stage.
It is an object of the present invention to provide an improved electrical machine for an internal combustion engine of the above-describe kind, which is switchable for operation as a starter or a generator of the internal combustion engine with simple means.
According to the invention the electrical machine is synchronous or asynchronous and is alternately operable as a starter or as a generator of the internal combustion engine. This electrical machine comprises a two-stage planetary gear device coupled to a shaft of the internal combustion engine, in which each stage includes a plurality of gears, and respective braking devices assigned to the two stages to halt a rotary motion therein. The two-stage planetary gear device includes means for operation with a different gear ratio in a starter mode than in a generator mode.
The electrical machine of the present invention, which alternately functions as a starter or a generator for an internal combustion engine, advantageously includes simple means for switchover between gear ratios optimally adapted to the operation of the electrical machine as a starter and as a generator respectively.
Desirable gear ratios, for example for the use of a claw pole machine (synchronous or asynchronous machine) as an electrical machine are a gear ratio range of 1.6 to 4 for the generator mode and 4 to 60 in the starter mode. The spread, that is, the ratio of the gear ratios to one another, should be at least 2.
The brake force can be exerted in a simple way, in particular by the engagement of a braking device with a ring gear of the planetary gear. Shoe brakes, lamination brakes or friction belt brakes can in particular be considered for the braking devices.
In a first preferred embodiment of the electrical machine, the planetary gear includes two sun wheels solidly connected to the engine shaft and two sets of planet wheels, each meshing with one of the sun wheels and with a ring gear, and the planet wheels of both sets are rotatably mounted on a planet carrier that in turn is solidly connected to a starter or generator shaft, in order to transmit a rotary motion to the generator shaft, or from the generator shaft to the planet carrier. In this construction, by braking one of the two ring gears, a rotary force can be transmitted between the sun wheel of the braked stage of the two-stage gear and the planet carrier, while the other stage rotates freely.
This construction makes an especially compact design possible, in which the dimensions of the two ring a gears are identical. This reduces the number of different components of the gear that are required and makes more-rational and more-economical production possible.
In a second preferred embodiment, the planetary gear includes two sun wheels, of which one is solidly connected to the engine shaft and one to the starter or generator shaft, and two sets of planet wheels, each meshing with one of the sun wheels and one of the ring gears. The planet wheels of the two sets are connected in pairs on a common axle in a manner fixed against relative rotation. In a variant of this embodiment, the ring gear of one stage can be omitted.
In a third preferred embodiment, the two-stage planetary gear includes two sun wheels, one of them solidly connected to the engine shaft and the other to a starter or generator shaft, and two sets of planet wheels, each meshing with one of the sun wheels; the planet wheels of the two sets mesh with one another in pairs. A planetary gear of this kind requires only one ring gear.
In the second and third embodiment, the second braking device preferably does not engage a ring gear but instead is arranged to block the planetary motion of the planet wheels, or in other words their rotation about the shafts.
To that end, the planet wheels of both sets are preferably mounted rotatably on a common planet carrier, and the second braking device engages this planet carrier.
To simplify the control of the planetary gear, a common adjusting device for actuating both braking devices is preferably provided, which has at least one working position in which the first braking device is open and the second is closed, one working position in which the second braking device is open and the first is closed, and an idling position in which both braking devices are open. These positions can be set or adjusted by a control element that is movable with one degree of freedom. This degree of freedom is preferably a rotation, so that the adjusting device can be actuated simply, for instance with the aid of arbitrary conventional electrical machines.
To assure a gentle transition between the two gear ratio states of the gear, each corresponding to one working position of the adjusting device, the adjusting device can preferably be moved past the idling position from one working position to the other.
It is also expedient that the adjusting device can be moved past one working position to a braking position, in which the braking device that is open in the working position begins to be braked. The term xe2x80x9cbegins to be brakedxe2x80x9d is understood to mean a state of the braking device in which the braking moment is other than zero, but is limited enough that an overload on the gear and the drive train is precluded. The complete closure of one braking device should be allowed by the adjusting device only whenever the other braking device is not also closed at the same time.
In a first preferred embodiment of the adjusting device, in which the braking devices are actuatable by adjusting motions parallel to one axle of the gear, the adjusting device includes two ramps, rotatable about this axle, for converting a rotary motion into an adjusting motion of the braking devices. To couple the actuation of the braking devices, it suffices for the two ramps to be connected in a manner fixed against relative rotation. An adjusting device of this kind is particularly suitable for use where lamination brakes are the braking devices.
In a second embodiment of the adjusting device, in which the braking devices are actuatable by an adjusting motion perpendicular to an axle of the gear, the adjusting device has at least one cam disk and levers, interacting with the cam disk, for converting a rotation of the cam disk into an adjusting motion of the braking devices. It is understood that each lever and thus each braking device may also be assigned its own cam disk. This embodiment is suitable in particular for use in conjunction with shoe brakes as the braking devices.
Further characteristics and advantages of the invention will become apparent from the ensuing description of exemplary embodiments.